The present invention relates to electromagnetic valve actuators in which the displacement of valves is controlled by energizing actuator electromagnets with currents having suitable waveforms, or pulse patterns.
Actuators of the type here under consideration may be used, for example, in place of conventional mechanical valve lifters for actuating automotive engine cylinder intake and exhaust valves. However, such valves may be employed in other types of power systems or fluid flow systems.
Known electromagnetic valve actuators include an armature shaft which contacts a valve stem to a valve head, bias springs which act on the armature shaft to urge it towards an intermediate position and electromagnets that are individually energizable to move the armature shaft, and thus the valve head, to either one of two end positions. These two end positions correspond, respectively, to a closed position in which the valve head mates with a valve seat and an opened position in which the valve head is spaced from the valve seat.
An example of such an electromagnetic valve actuator is disclosed in commonly owned U.S. Pat. No. 5,782,454, the entire disclosure of which is incorporated herein by reference.
In the operation of such a valve actuator, the valve head will remain in one of its end positions as long as one of the electromagnets is producing a magnetic field sufficient to hold the armature in that position against the force of the bias springs. Therefore, a significant current must be supplied to the energized electromagnet for as long as the valve head is to be maintained in the opened or closed position. As a result, a considerable amount of electrical power would be consumed in the operation of one of these valve actuators. In systems employing a plurality of valves, which may be up to 48 valves in some automotive engines, the current consumption level is proportionally higher.
As a general rule, it is preferable that movement of a valve between its opened and closed position occur in the shortest time possible. The speed of movement for a given assembly depends on the level of current supplied to the electromagnetic being energized, which in turn determines the acceleration experienced by the valve and actuator components which move as a unit with the valve.
However, the higher the valve displacement speed, the greater the impact associated with arrival of the valve at its end position and the greater the likelihood that the valve will experience some bounce at the end of its movement. These factors adversely affect the performance of the associated engine.